PB2477: INTEGRATION OF OPTICAL GENOME MAPPING IN DAILY CYTOGENETICS LABORATORY ROUTINE.
Authors: Álvaro Díaz González, Gayane Avetisyan, Cristian Garcia-Ruiz, José Vicente Gil, Marta Santiago, Juan José Domínguez-García, Marta Llop, Eva Barragan, Maria Leonor Senent Peris, Javier DE LA Rubia, José Cervera, Esperanza Such
Journal: HemaSphere (2023)

Topic: 23. Hematopoiesis, stem cells and microenvironment Background: The gold standard technique for cytogenetics diagnosis is chromosome banding analysis (CBA). However, there is a limitation of the standard cytogenetics procedures. CBA requires metaphases and the alteration needs a minimum size of 5 Mpb to be detected. Optical Genome Mapping (OGM) is a novel high-throughput diagnostic method that may overcome the drawbacks of standard cytogenetic approaches. OGM can detect structural variants (SVs), copy number variations (CNV), and balanced or unbalanced rearrangements from 500 base pairs in a single assay. Aims: This study aimed to assess the application of OGM in daily cytogenetics laboratory workflow and compare it with the standard approach. Methods: Karyotype was performed from bone marrow following standard procedures. FISH was executed in selected cases according to the diagnostic guidelines. OGM was performed following the manufacturer’s protocol (Bionano Genomics). Analysis of the samples was performed with the Bionano Access software. The recommended filters were used. All clinically significant alterations were reported. Results: A total of 111 patients remitted to the Cytogenetic Laboratory of Hospital La Fe were included: 4 aplastic anemia (AA), 29 acute lymphoblastic leukemia-B (B-ALL), 7 T-ALL, 28 acute myeloblastic leukemia (AML), 29 myelofibrosis (MF), and 14 myelodysplastic neoplasms (MDS). Conventional karyotype was informative in 85/111 (76%) patients, being normal in 45 (40%) patients, abnormal in 40 (36%), and non-informative in the remaining 27/111 (24%) cases. Regarding those with unsuccessful karyotypes, most of them were MF (n = 12) and ALL (n = 7). FISH was performed complementary in 74/111 (65%) patients being abnormal in 40/74 (54%). These are the results highlighted by hematological neoplasm with assessable OGM analysis: • AA (n = 4): CBA was normal in 2 patients and unsuccessful in two. OGM was assessable in all patient’s and it did not detect any relevant alteration. • B-ALL (n = 29): 12/29 patients had a previously abnormal CBA. OGM confirmed the same alterations in 5/12 and detected additional alterations in 5/12. OGM redefined the karyotype in 2 patients who showed a masked hypodiploidy. OGM showed cryptic alterations in 9/11 patients with normal CBA, such as deletions in IKZF1, PAX5, and CDKN2A/B. • T-ALL (n = 7): OGM detected an abnormal result in all patients including rearrangements in of DDX3X::MLLT10, ETV6::FOXO1, PICALM:: MLLT10 and STIL::TAL in 6/7 patients. • AML (n = 28). OGM redefined the CBA in 11 patients (previous CBA: 3 abnormal, 7 normal, and 1 unsuccessful). Of note, OGM detected 4 patients with NUP98::NSD1 rearrangement and 2 patients with a partial tandem duplication of KMT2A cryptic to CBA. • MF (n = 29). OGM characterized all cases with unsuccessful CBA (11/29) from PB being normal in 8/12 and abnormal in 3/11 including high-risk alterations defined by current prognostic index like MIPSS70v2+. • MDS (n = 14). OGM redefined the karyotype in 7/14 patients including a cryptic rearrangement of MECOM::CCDC26. All novel alterations were conveniently confirmed by FISH o molecular biology. OGM was unsuccessful in 6/111 (5.4%) patients due to the low cellularity or low quality of the sample. Finally, OGM did not detect the alterations showed by CBA in two patients with MDS due to CBA being performed in BM and OGM in PB without blasts. Summary/Conclusion: In summary, this series demonstrates the feasibility of performing OGM in daily routine and confirms that it can overcome the limitations of standard approaches, especially in patients with unsuccessful karyotype or cryptic alterations.Keywords: Diagnosis, Prognosis, Cytogenetics